1. Field of the Invention
The present invention relates to an ultrasonic probe in which a group of piezoelectric elements oscillates in the short-axis direction of the probe to obtain a three-dimensional image (hereinafter called a “short-axis oscillating probe”) and, in particular, to a short-axis oscillating probe of a simple configuration that uses a stepping motor.
2. Description of Related Art
A short-axis oscillating probe that is known in the art obtains a three-dimensional image by electronically scanning a group of piezoelectric elements in the long-axis direction of the probe and also by mechanically scanning (oscillating) the group of piezoelectric elements in that short-axis direction (see Japanese Patent Publication No. 7-38851 and Japanese Patent Laid-Open Publication No. 2003-175033). Since components such as wiring (connective wires) and scan circuitry of this type of short-axis oscillating probe can be configured simply, in comparison with a matrix type of probe in which piezoelectric elements are arrayed horizontally and vertically to provide a two-dimensional scan, this probe can be implemented easily.
A prior-art example of a short-axis oscillating probe (see Japanese Patent Publication No. 7-38851) is shown in FIG. 5A, where FIG. 5A is a section taken along the long-axis direction (X-X direction) of the probe and FIG. 5B is a section taken along the short-axis direction (Y-Y direction) thereof.
This prior-art short-axis oscillating probe is provided with a group of piezoelectric elements 101, a rotational mechanism portion 102, and a rotational angle detection mechanism 103. The group of piezoelectric elements 101 is arrayed on a base 104 to which backing material is attached, with the widthwise direction of the plurality of narrow card-shaped piezoelectric elements 101a aligned in the long-axis direction and also the lengthwise direction thereof aligned in the short-axis direction. This backing material is affixed on top of the base 104, which is formed of a plastic material in a convex dome shape in the long-axis direction, with the configuration being such that the group of piezoelectric elements 101 is curved outward in the long-axis direction.
A flexible substrate 105 that has been connected electrically to the group of piezoelectric elements 101 over the entire region of the probe in the long-axis direction thereof is lead out downward from one end side of the probe in the short-axis direction, as shown in FIG. 5B. In this case, a conductive path 105a of the flexible substrate 105 is connected electrically to a drive electrode of each piezoelectric element 101a. 
The rotational mechanism portion 102 shown in FIG. 5A is formed of a retaining plate 106 of a metal material, a case 107, a segment-shaped first bevel gear 108a, a second bevel gear 108b, a control shaft 109, and a stepping motor 110. The retaining plate 106 has leg portions 106a and 106b on the lower surface thereof on both edge sides in the long-axis direction, and the base 104 holding the group of piezoelectric elements 101 consisting of the plurality of piezoelectric elements 101a is affixed to the upper surface thereof. In the leg portions 106a and 106b, center shafts 111a and 111b that penetrate through the leg portions 106a and 106b are supported in rotation by bearings 111c and 111d in the long-axis direction (on the line X-X in the horizontal direction of the case 107), with the leg portions 106a and 106b being provided to be freely rotatable about the center shafts 111a and 111b. 
The case 107 is formed to be concave in section with the upper surface thereof being open, and projecting ends of the center shafts 111a and 111b that bear the leg portions 106a and 106b are affixed to peripheral walls of the case 107. A slit 112 is formed in the long-axis direction of the bottom wall of the case 107, as shown in FIG. 5B, and the flexible substrate 105 that is connected to the group of piezoelectric elements 101 is lead out to the exterior of the case 107 therethrough. A material such as a plastic material is embedding in the slit 112 to seal the same.
The first bevel gear 108a of a segment shape is affixed by screws or the like to the inner surface of the leg portion 106a that is one of the leg portions provided on the retaining plate 106, below the center shaft 111a that passes therethrough and is supported in rotation thereby, and has teeth in an arc (a fan shape) with a peak thereof at the lower end in the vertical direction. The second bevel gear 108b is supported rotatably on the free end of the control shaft 109 that is aligned in the vertical direction perpendicular to the center shafts 111a and 111b (the line X-X), engages with the first bevel gear 108a, and rotates in the horizontal direction. The control shaft 109 is lead out of the case 107 from the bottom wall of the case 107 and is sealed by a bearing seal member 114, and the other end thereof is linked to the stepping motor 110 by means such as a gear linkage.
The rotational angle detection mechanism 103 is configured as an optical encoder (see FIG. 6) and consists of an optical rotary plate 103a, which is integral with the control shaft 109, and an optical counter 103b, which is U-shaped in section and into which the outer periphery of the optical rotary plate 103a is inserted. A large number of small holes 103c are provided around the outer periphery of the optical rotary plate 103a, and the optical counter 103b has a light-emitting portion and a light-receiving portion on leg portions that face the optical rotary plate 103a. 
Light that has been transmitted through one of a number of small holes 103c from the light-emitting portion of the optical counter 103b is detected by the light-receiving portion, and the reference position of the group of piezoelectric elements 101 is detected by counting the number of times that light is transmitted therethrough. This reference position is positioned on the centerline that bisects the short-axis direction, by way of example, and is detected by means of a number of optical or magnetic sensors. Note that a cover that encloses the group of piezoelectric elements 101 is provided for the case 107, the group of piezoelectric elements 101 and other components are hermetically sealed therein, and the interior thereof is filled with an ultrasound transmission medium such as oil.
In the thus-configured probe of the prior art, the rotation of the second bevel gear 108b of the rotational mechanism portion 102 horizontally to left and right causes the first bevel gear 108a that is engaged therewith to rotate and oscillate with respect to the vertical plane so that the peak thereof inclines upward to the left or right from the center. In other words, the peak of the first bevel gear 108a rotates and oscillates to the left and right of the vertical direction acting as center. Thus the leg portions 106a and 106b of the retaining plate 106 rotate and oscillate to the left and right with respect to the center shafts 111a and 111b, and also the group of piezoelectric elements 101 rotate and oscillate to the left and right in the short-axis direction, in the opposite directions thereto. In addition, the rotational angle of the group of piezoelectric elements 101 in the short-axis direction is detected by the rotational angle detection mechanism 103, ensuring that biological information is obtained from precise positions of the object to be detected (organism).